The present invention relates to a novel magnetoresistive effect head and a magnetic recording and reproducing apparatus using the same, and more particularly to a magnetoresistive effect head suitable for a recording head for reproducing information of a magnetic recording medium by utilizing a giant magnetoresistive effect and a magnetic recording and reproducing apparatus using the same.
A reproducing head as well as a recording head are mounted on a magnetic recording and reproducing apparatus, and an AMR (Anisotropic Magnetoresistive) head which utilizes an anisotropic magnetoresistive effect has been proposed as a reproducing head. In the AMR head, since it is required to suppress a Barkhausen noise generated by the head to prevent a malfunction of the magnetic recording and reproducing apparatus, a magnetic domain control layer for maintaining the magnetoresistive effect layer in a single magnetic domain state is provided in the head.
In a first generation AMR head having the magnetic domain control layer provided therein, a magnetic domain control system called a patterned exchange as disclosed in U.S. Pat. No. 4,663,685 is adopted. In this system, a magnetic domain control layer formed of an antiferromagnetic film is patterned, the patterned magnetic domain control layer is stacked only in end regions of a magnetoresistive effect film (MR film), this region is maintained in a single magnetic domain state, and a central magnetic sensing area (a region sandwitched between a pair of electrodes for transducing a change in a magnetic field to an electrical signal) of the MR films is induced to a single magnetic domain state.
It has been reported that the AMR head adopting the patterned exchange system can improve a sensitivity by increasing a spacing of the magnetic domain control layers to be larger than a spacing of electrodes, as disclosed in an article of the Institute Journal of the Magnetics Society of Japan, Vol. 19, page 105 (1995).
In a second generation AMR head, a hard biasing system is adopted as disclosed in JP-A-3-125311 in order to facilitate the manufacture as compared with the first generation AMR head. In this system, both ends of the MR film extended to the end regions are cut off, the MR film is formed only in the magnetic sensing area, and the magnetic sensing area is maintained in a single magnetic domain state by a magnetic field generated by a permanent magnet. It has also been proposed to use a lamination of ferromagnetic films and antiferromagnetic films instead of the permanent magnet as disclosed in JP-A-7-57223.
On the other hand, as a next generation high sensitivity MR head which takes place of the AMR head, a spin valve head utilizing a giant magnetoresistive effect has been proposed as disclosed in JP-A-4-358310. The spin valve head comprises, as a magnetoresistive effect film, a first ferromagnetic film whose direction of magnetization is change by a magnetic field from a magnetic recording medium, a second ferromagnetic film whose direction of magnetization is fixed and a nonmagnetic conductive film inserted between the first and second ferromagnetic films. The second ferromagnetic film is stacked on an antiferromagnetic film or a permanent magnet which serves to fix the direction of magnetization of the second ferromagnetic film. In order to enhance an output of the spin valve head, a dual type of spin valve head has been proposed as an application of the spin valve head as disclosed in JP-A-5-347013. The dual spin valve head comprises, as a magnetoresistive effect film, a first ferromagnetic film whose direction of magnetization is changed by a magnetic field from a magnetic recording medium, second and third ferromagnetic films whose directions of magnetization are fixed, a nonmagnetic conductive film inserted between the first ferromagnetic film and the second ferromagnetic film and a non-magnetic conductive film inserted between the first ferromagnetic film and the third ferromagnetic film. The second ferromagnetic film and the third ferromagnetic film are stacked above and below the first ferromagnetic film to oppose to the first ferromagnetic film, and the second and third ferromagnetic films are directly stacked on an antiferromagnetic films or permanent magnet which serves to fix the directions of magnetization of the second and third ferromagnetic films.
In those spin valve heads, since the direction of magnetization is changed by the magnetic field from the magnetic recording head in the first ferromagnetic film, it is required to maintain the first ferromagnetic film in the single magnetic domain state.
The spin valve head has been known as one which takes place of the AMR head, but in the prior art spin valve head which uses the hard biasing system, a reproduced waveform may be distorted or a reproduced output may be dropped by a strength of the magnetic domain control layer.
For example, when a strength of the magnetic domain control layer is not enough to bring the first ferromagnetic film to the single magnetic domain state, the reproduced waveform may be distorted and the magnetic recording and reproducing apparatus may malfunction. This distortion is usually called a Barkhausen noise and it has been proved that a cause of the generation of this noise is discontinuous movement of magnetization at the ends of the first ferromagnetic film. This Barkhausen noise is easier to be generated in the spin valve head than in the AMR head. This is because, in the spin valve head, the operation is mainly conducted while the magnetization of the first ferromagnetic film is oriented laterally and in the AMR head, the operation is mainly conducted while the magnetization of the MR film is inclined to approximately 45 degrees. Namely, in the spin valve head, when leakage magnetic fields (positive and negative) of the magnetic recording medium are applied, the magnetization at the ends of the first ferromagnetic film are vertically inverted. This is because a static energy is high when the magnetization at the ends of the first ferromagnetic film is directed laterally while the strength of the magnetic domain control layer is not sufficient so that the oblique upward or oblique downward direction of magnetization is in an instable state. On the other hand, in the AMR head, since the magnetization at the ends of the first ferromagnetic film is always oriented obliquely, the discontinuous movement of the magnetization as observed in the spin valve head does not take place.
When the strength of magnetization is sufficient to a certain extent and the spacing of the electrodes of the spin valve head is reduced to increase a track density of the magnetic recording and reproducing apparatus, an output (sensitivity) per unit electrode spacing abruptly decreases. The output of the spin valve head increases basically in proportion to the electrode spacing. This is because the longer the areas in which the voltage changes are serially connected, the larger is the overall change in the voltage. However, when the electrode spacing is simply reduced in the prior art hard bias system spin valve head, the output (sensitivity) per unit electrode spacing abruptly decreases. Particularly when the electrode spacing is reduced to 2 .mu.m or less, the sensitivity of the head is reduced to 90% or less of its inherent sensitivity. A cause for the reduction of the sensitivity is the low sensitivity at the left and right end regions of the first ferromagnetic film by the influence of the magnetic domain control layer stacked below the electrode. Accordingly, as the electrode spacing is reduced and the influence by the magnetic domain control layer increases, a proportion of the high sensitivity central area is reduced, and as a result, the sensitivity is reduced. Accordingly, in the prior art hard biasing system spin valve head, when the electrode spacing is simply reduced, the sensitivity is abruptly reduced and the malfunction of the magnetic recording and reproducing apparatus increases. As a result, it is difficult to increase the track density of the magnetic recording and reproducing apparatus.
Further, when the strength of the magnetic domain control layer is sufficient to a certain extent, the head output is abruptly reduced as the strength of the magnetic domain control layer increase even if the electrode spacing is kept unchanged. For example, when a longitudinal bias ratio which is a factor to indicate the strength of the magnetic domain control layer is 2, the head output is reduced to approximately 60% of its inherent output. When the magnetic domain control layer is the permanent magnet, the longitudinal bias ratio is represented by a ratio of a product (Br.multidot.t) of a remanent magnetic flux density Br of the permanent magnet and a film thickness t, and a product (Bs.multidot.t) of a saturation magnetic flux density Bs of the first ferromagnetic film in the spin valve head and the film thickness t. When the magnetic domain control layer is the stacked layer of the ferromagnetic films and the antiferromagnetic films, the longitudinal bias ratio is represented by a ratio of a product (Bs.multidot.t) of the saturation magnetic flux density Bs of the ferromagnetic film in the magnetic domain control layer and the film thickness t, and a product (Bs.multidot.t) of a saturation magnetic flux density Bs of the first ferromagnetic film in the spin valve head and the film thickness t.
Further, since the magnetic domain control layer is manufactured in a separate process from that of the first ferromagnetic film, the strength of the magnetic domain control layer, that is, the longitudinal bias ration includes a variation to some extent. As a result, the head output includes a variation. Further, as described above, since the Barkhausen noise is generated if the strength of the magnetic domain control layer is insufficient, the strength of the magnetic domain control layer is set to be somewhat larger than a required value. As a result, the output is reduced.
In the prior art hard bias system spin valve head, since the head output largely depends on the strength of the magnetic domain control layer, the output is reduced and the malfunction of the magnetic recording and reproducing apparatus increases when the strength of the magnetic domain control layer is high.